optimization of operating plant performance in view of...

Authors: Florian Röhr Dr. Andreas Feldmüller Siemens AG Energy Sector Service Division

Optimization of operating plant performance in view of new market conditions

POWER-GEN Europe 2012, Cologne, Germany June 12-14, 2012

www.siemens.com/energy

AL: N; ECCN: N

© Siemens AG 2012. All rights reserved. of 21

Table of Contents

1 Abstract .................................................................................................................. 3

2 A view on the current European energy market..................................................... 4

3 Improving hot start-up time with the “Hot Start on the Fly” ................................. 8

4 Improving cold start-up time with the “Fast Release to Nominal Speed” ........... 13

5 Low load study of SPP with steam extractions .................................................... 16

6 Future prospects ................................................................................................... 19

7 Disclaimer ............................................................................................................ 20

AL: N; ECCN: N


1 Abstract

The increasing share of renewable energy in Europe will continue to change the operational

profile of the plants. Steam and combined cycle power plants which have been built for base

load operation are facing new market conditions:

less operating hours

less megawatt generated due to increasing part load operation

increased number of starts and fast start-up requirements

increasing control reserve market

With decreasing megawatts generated, the utility will face the need to generate the remaining

megawatts most efficient and to be available whenever the energy market is paying premium

prices for generated energy or control reserve. The paper will point out the changing market

conditions and the relevance for the operating fleet.

AL: N; ECCN: N


2 A view on the current European energy market

Each MWh which is produced by renewable energy sources and sold preferentially via the

Merit Order, substitutes the production of this particular MWh in a conventional fossil power

plant. Beyond that, lowers the inexpensive renewable energy production (billions of subsidies

not considered) the floated electricity price at the spot markets (short-term) and on the long

run also on the future markets. Power plant operators will most probably face the problem in

the nearer future to sell less MWh at a lower price level, assuming that the current business

framework of the energy market is not changed.

But the greater the share of volatile renewable energy sources like wind or solar power, the

greater will be the demand for flexibility in the remaining energy system. Effective smart

grids and affordable energy storages are still visions of the future, so the balance between

demand and renewable production -residual load- has to be taken mainly by the fossil power

generation.

Figure 1 shows a comparison regarding base load hours, number of starts and residual load

ranges of the year 2010 to a fictive scenario AT40 RE. The AT40 RE scenario assumes a 40%

share of renewable energy (RE) production at a constant demand level (AT) compared to the

year 2010. It was developed and published by the VDE (Association for Electrical, Electronic

& Information Technologies, Germany). Therefore the scenario is slightly outbalancing the

target of at least 35% share of renewable energy production in 2020 given by the German

Government.

AL: N; ECCN: N


Fig. 1: Comparison of key parameter in 2010 vs. a 40% renewable scenario

The shift in lower ranges of residual load refers to the increasing production capacity of

renewable energy and as a result of it, an intense need for flexibility. In 2010 for instance the

residual load range down to 35-40 GW was required only 25 times. In the AT40 RE scenario

this will happen over 315 times. The residual load range 0-2 GW will occur in 2020 more

than 45 times - which basically means that nearly no fossil power generation is needed at all

during these market conditions.

This leads to dramatic drop of fossil plants which are currently operating only in base and mid

load operation. Future operation will be dominated by increased number of starts, low part

load operation and fast ramps serving the strained control reserve market.

The energy providers are facing the challenge of fewer operating hours per annum, dropping

average electricity prices and increasing carbon allowances costs. The current market

conditions make business plans of new efficient plants less attractive, slowing down new

apparatus builds as can be seen in whole Europe. For assets plants, the situation in the UK is

already challenging, due to the fact that the spark spread is in a low single-digit range. Some

energy providers mothballed their power plants.

AL: N; ECCN: N


The clean spark spread is the theoretical gross margin of a gas fired power plant from selling

a unit of electricity, having bought the fuel required to produce this unit of electricity and the

necessary carbon allowances. All other costs (operation and maintenance, capital and other

financial costs) must be covered from the clean spark spread (see Figure 2).

Fig. 2: The Clean Spark Spread (CSS)

On the other hand the energy market offers high revenues when participating in the high price

periods like the one in February 2012 in Germany. Russia cut the gas export to Southern

Germany by almost 30%. Gas fired plants in Southern Germany were throttled or even

stopped. In addition, wind energy production in these days was low due to weather

conditions. This lead to decent electricity prices at the European Energy Exchange EEX (see

Figure 3) and correspondingly to a healthy clean spark spread (see Figure 4).

Fig. 3: Average electricity prices in February 2012, Epexspot, EEX

AL: N; ECCN: N


Fig. 4: The Clean Spark Spread (CSS) of a common CCPP

The authors are convinced that asset plants, which have low transcription cost, are able to be

cost-effective despite declining utilization grades, if they can realize their whole flexibility

potential and take part in high price periods or attractive markets like the control reserve

markets. The following solutions should support this formation.

AL: N; ECCN: N


3 Improving hot start-up time with the “Hot Start on the Fly”

As discussed in section 1 of this paper, the prospective future load regime will be defined by

the residual load demand resulting by the volatile renewable energy generation. For many

CCPP this will lead to an intense daily cycling mode with up to two starts per day, as the

morning and evening demand need residual load while during sunny days the residual load

disappears. Hence, all measures which reduce the start-up time as well as the start-up

efficiency will gain in importance.

Siemens Energy has developed a fast cycling upgrade for CCPP to meet these requirements.

The so called Hot Start on the Fly which was successfully introduced in new plants as well as

in plant modernization incorporates a revised start-up concept of the overall plant - with a

parallel start-up of the gas turbine and the steam turbine. The gas turbine will be started and

loaded without any hold in part load operation (see Figure 5). When the first steam is

generated by the Heat Recovery Steam Generator, the steam turbine will be also started and

loaded during continuous temperature and pressure increase - thus the critical time were cold

steam meets hot components is limited to an absolute minimum. Validation shows that the

new start-up concept can be implemented in compliance with the existing limitation factors of

the plant.

Fig. 5: A typical Hot Start on The Fly

AL: N; ECCN: N


With the Hot Start on the Fly solution, a hot start-up time below 30 min could be achieved in

a new apparatus CCPP. In an asset plant a potential start-up time reduction of approx. 20-40

min can be granted and will be evaluated in a specific site assessment due to individual plant

set-ups.

The following example shows a benefit examination in a European asset plant. Both the asset

and the reference plant do have a SGT5-4000F(6) with a SST5-5000 steam turbine in single

shaft configuration. All shown trends are based on real data.

As a result of a site assessment, a potential time saving of 25 min compared to a common hot

start could be granted when using the Hot Start on the Fly. Figure 6 shows a comparison of a

typical hot start and Hot Start on the Fly. The both trends were scaled to zero time when the

inlet guide vanes of the gas turbines are fully open and bypass stations closed - the total plant

literally reaches base load. As mentioned before, due to the new start-up philosophy the Hot

Start on the Fly does not need any waiting times of the gas turbine in less efficient part load

operation. Therefore all flat periods of the blue line (Block load) can potentially be deleted.

The red-hatched area under the red line (gas consumption) illustrates the additional

consumption of a traditional hot start. To go a bit deeper into detail: during the common hot

start of the asset plant, 35.000 Nm³ of gas were consumed and 128 MWh electricity were

generated. The reference plant with the Hot Start on the Fly uses 23.000 Nm³ of gas,

generating 94 MWh during the start-up process.

AL: N; ECCN: N


Fig. 6: Comparison of a common hot start and the Hot Start on The Fly

To regain the gap of 34 MWh compared to the asset plant, the reference plant needs 5 minutes

of efficient base load operation with another 5.600 Nm³ of gas. So if the same electricity

output (128 MWh) should be the objective, the Hot Start on the Fly needs still 6.600 Nm³ less

gas.

With this amount of saved gas, approximately 6 minutes of base load operation is possible

with best efficiency. Thus, every Hot Start on the Fly generates approximately 40 MWh

(green hatched area) more - per start (see Figure 7).

58

32

HoF plant

128 MWh

128MWh

Asset plant

AL: N; ECCN: N


Fig. 7: Additional operation from saved gas in best efficiency area

In Figure 8 a set of curves can be seen which show the commercial benefit of Hot Start on the

Fly in connection of electricity price and number of starts performed. The lower set of curves

reflecting the average area of energy exchange prices across Europe in the past two quarters.

To show the benefit in a high price season as it was in Germany in February 2012 please refer

to the upper set of curves.

Quelle: Trianel GmbH, 09/2011

58

32 HoF plant

Asset plant

AL: N; ECCN: N


Fig. 8: Commercial benefit of the Hot Start on the Fly

To summarize, the Hot Start on the Fly is the most economic way to start-up the plant. It can

be selected as a start-up in the unit coordination of the plant. In an environment of low spark

spreads and as a result of it less operating hours, plant operators are able to use periods of

strong demand for residual load to maximize plant profit.

AL: N; ECCN: N


4 Improving cold start-up time with the “Fast Release to Nominal

Speed”

With less base load operation in volatile markets, plants are often forced so stay offline for

more than two days. During this time the steam turbine naturally cools down and than

demands an extended heat soak time during an upcoming start - which means the gas turbine

has to be operated in less efficient part load operation. With the solution “Fast Release to

Nominal Speed” for HP barrel type turbines, the waiting time can be reduced significantly.

To secure a safe and gentle ramp up to nominal speed, superheated steam in all areas of the

HP turbine must be present. For this different pressure and temperature measurements will be

monitored and criteria were developed. The main criteria which need to be fulfilled are:

The casing inlet temperature and casing temperature need to be above the saturated steam

temperature. The cover and base casing temperatures (50% measurements) need to be 10K or

less below the saturated steam temperature (see Figure 9).

Fig. 9: Release criteria for Siemens HP drum type turbines

When all of these criteria are achieved, the release for nominal speed is given to the operator.

AL: N; ECCN: N


Fig. 10: Parameters during heat soak time

Figure 10 shows operational parameter from the evaluation of the “Fast Release to Nominal

Speed” in a European power plant. Like shown, criteria one and two were achieved in three

respectively two minutes after warm-up speed. Criteria four and five were already achieved

during the acceleration. The third criteria, superheated condition at cover and base casing

temperatures, need up to 40 minutes until fulfillment, due the thick components.

To shorten the start-up process, the measurement of the 50% HP cover and base casing

temperature (MAA50CT051/52) which have severe time delays with respect to the increasing

steam temperature will be replaced by a new temperature measurement. It is possible to

identify a new, fast responding location to check the steam temperature and to implement the

new measurement at this position. All validation runs indicated that the new measurement

reliably indicates a superheated steam condition. In Figure 11 it is shown (green line) that the

new criteria is achieved nearly simultaneous (after three minutes) with criteria one and two.

AL: N; ECCN: N


Fig. 11: Improvement of new criteria

With the “Fast Release to Nominal Speed” the cold start can be shortened by approximately

30 minutes and gas of up to 17.500 Nm³ (based on a typical Siemens 400 MW class CCPP)

can be saved.

AL: N; ECCN: N


5 Low load study of SPP with steam extractions

One main pillar of Europe’s energy system is the electricity generation made by solid fuels

such as coal and oil. Roughly one third of the European power demand is covered by Steam

Power Plants (SPP) fired with the mentioned fuels. It is obvious that these power plants also

have to contribute in the fluctuating residual load.

The low load study presented as follows was carried out in a 400 MW class hard coal fired

SPP in continental Europe. The Siemens steam turbine is an SST5-6000 configuration with

special design of the intermediate and low pressure turbine to allow for six extractions for

condensate respectively feed-water preheating and to provide process steam as well as steam

for district heating. On the one hand this kind of power plants have to fulfill the contractual

commitment to deliver process steam and district heating to their customers, but on the other

hand electricity generation is technically and commercially fluctuating. Facing these

conflicting targets, a study was performed to investigate new operation conditions of the

plant. One objective of the study was to investigate permanent operation in a scenario of

minimized electricity generation while maintaining heating and process steam delivery.

Figure 12 shows the investigated low load scenarios in correlation with preheater in or out of

service and temperatures of hot reheat steam (t RH) and extracted steam flow (t F),

Fig. 12: Different investigated low load scenarios

AL: N; ECCN: N


To give a release for permanent operation in these scenarios, the following aspects were

investigated:

Maximum HP exhaust temperature

To maintain steam deliveries of a certain pressure for process and district heating, the IP

control valves need to be throttled to assure a defined minimum pressure at the extractions. As

a result of this a higher back pressure in the HP turbine takes place compared to the normal

sliding pressure operation. Thus the HP exhaust temperature might increases to a maximum

allowable value in stationary operation. In addition the maximum gradient for transient

operation needs to be considered.

Maximum IP exhaust temperature

The maximum permissible IP exhaust temperature was calculated with state of the art

engineering codes. The analysis, which considered the impact of this measure to all related

turbine parts (casing, shaft, blading and cross over pipes), resulted in an increase of the

permissible temperature.

Maximum IP differential temperatures

The specific design of the IP applies a sealing wall within the casing having steam of different

temperatures on both sides of this element. As a protection for high differential temperatures

at this wall, a thermal isolation was part of the original design. An extreme low load operation

would change the temperatures at this element as far as a deformation process might be

started. The new temperature conditions in low load operation needed to be simulated with

the finite element method.

Erosion

Another field of the study was the aspect of corrosion due to erosion. Droplet impact erosion

for instance emerges from the impact of water droplets on the leading edge of the LP blades

carried by the steam mass flow. For the evaluation of risk exposure a new erosion factor

needed to be determined for each LP stage.

AL: N; ECCN: N


Thrust

As the pressures and the steam flows in the turbine shall be changed for the new operating

conditions, the axial thrust has to be analyzed and compared with the allowables of casing

fixings and the rotor thrust bearing capabilities.

As one result of the study, which was performed by an engineering team including experts in

thermodynamics, mechanics and blade design, a considerable lower electricity load could be

granted without violating existing safety margins. To implement the new operating conditions

and to ensure a safe permanent low load operation, recommendations of I&C changes

(warning & alarm values) were given as part of the study.

AL: N; ECCN: N


6 Future prospects

When the future markets will reward even higher flexibility, it might be commercially

attractive to accept a reduction of component life in exchange of this flexibility.

The priority of the renewable energy generation in the merit order is by nature consequential -

the generation of renewables is environment friendly and has no fuel costs. Nevertheless,

leaving only a reduced number of operating hours and the burden of volatile residual loads

and its consequences to the remaining fossil fleet without sufficient commercial compensation

cannot be the final solution. It is expected that the design of the energy markets in Europe will

change in the years to come, which will lead to risks, but also opportunities for fossil plants.

Like the examples shown in this paper, Siemens Energy Service will continue to develop

customized solutions to strengthen the competiveness of fossil fired power plants.

AL: N; ECCN: N


7 Disclaimer

These documents contain forward-looking statements and information – that is, statements

related to future, not past, events. These statements may be identified either orally or in

writing by words as “expects”, “anticipates”, “intends”, “plans”, “believes”, “seeks”,

“estimates”, “will” or words of similar meaning. Such statements are based on our current

expectations and certain assumptions, and are, therefore, subject to certain risks and

uncertainties. A variety of factors, many of which are beyond Siemens’ control, affect its

operations, performance, business strategy and results and could cause the actual results,

performance or achievements of Siemens worldwide to be materially different from any

future results, performance or achievements that may be expressed or implied by such

forward-looking statements. For us, particular uncertainties arise, among others, from changes

in general economic and business conditions, changes in currency exchange rates and interest

rates, introduction of competing products or technologies by other companies, lack of

acceptance of new products or services by customers targeted by Siemens worldwide,

changes in business strategy and various other factors. More detailed information about

certain of these factors is contained in Siemens’ filings with the SEC, which are available on

the Siemens website, www.siemens.com and on the SEC’s website, www.sec.gov. Should one

or more of these risks or uncertainties materialize, or should underlying assumptions prove

incorrect, actual results may vary materially from those described in the relevant forward-

looking statement as anticipated, believed, estimated, expected, intended, planned or

projected. Siemens does not intend or assume any obligation to update or revise these

forward-looking statements in light of developments which differ from those anticipated.

Trademarks mentioned in these documents are the property of Siemens AG, its affiliates or

their respective owners.

AL: N; ECCN: N


Published by and copyright © 2012: Siemens AG Energy Sector Freyeslebenstrasse 1 91058 Erlangen, Germany

Siemens Energy, Inc. 4400 Alafaya Trail Orlando, FL 32826-2399, USA

For more information, please contact our Customer Support Center. Phone: +49 180/524 70 00 Fax: +49 180/524 24 71 (Charges depending on provider)

E-mail: [email protected]

All rights reserved. Trademarks mentioned in this document are the property of Siemens AG, its affiliates, or their respective owners.

Subject to change without prior notice. The information in this document contains general descriptions of the technical options available, which may not apply in all cases. The required technical options should therefore be specified in the contract..

optimization of operating plant performance in view of...

Documents